AQA GCSE Biology: Diseases Caused by Pathogens

For GCSE you need to know a set of named diseases, one or two for each type of pathogen, including their symptoms, how they spread and how spread is reduced. This guide works through them by pathogen type. For each, the pattern is the same: what it does, how it passes on, and how to stop it.

Viral diseases

Measles causes a fever and a red skin rash. It spreads by inhaling droplets from sneezes and coughs, and its spread is reduced by vaccination (most young children are vaccinated) and isolation. It is serious and can be fatal if complications such as pneumonia develop.

HIV begins with a flu-like illness, then often shows no symptoms for years. It spreads by sexual contact and by the exchange of body fluids, such as blood when drug users share needles. It is controlled with antiretroviral drugs, and spread is reduced by using condoms and not sharing needles. HIV attacks immune cells, and if it is not controlled it leads to AIDS, the late stage, when the immune system is so damaged that the body can no longer fight off other infections or cancers.

Tobacco mosaic virus (TMV) is a plant disease that causes a mosaic pattern of discolouration on leaves. Because this reduces the amount of chlorophyll, less photosynthesis happens, so the plant grows poorly. It spreads by direct contact between plants, and its spread is reduced by removing infected plants and by washing tools in disinfectant.

Bacterial diseases

Salmonella causes food poisoning: fever, abdominal cramps, vomiting and diarrhoea, caused by the toxins the bacteria release. It spreads through food that is contaminated or prepared in unhygienic conditions. In the UK, poultry are vaccinated against it to reduce the bacteria in chicken and eggs, and good hygiene when preparing food helps too.

Gonorrhoea is a sexually transmitted disease causing a thick yellow or green discharge and pain on urinating. It spreads by sexual contact, and its spread is reduced by using condoms and by treatment with antibiotics, although many resistant strains have now appeared, so it is harder to treat than it once was.

Fungal diseases

Rose black spot is caused by a fungus. It produces purple or black spots on leaves, which then often turn yellow and drop early. This reduces photosynthesis, so the plant grows less well. It spreads through the environment by water and wind, and its spread is reduced by using fungicides and by removing and destroying affected leaves.

Protist diseases

Malaria is caused by a protist. It causes recurring episodes of fever and can be fatal. The protist's life cycle involves the mosquito, which acts as a vector: a mosquito feeds on infected blood, then passes the protist on when it bites another person. Its spread is reduced by stopping mosquitoes breeding (for example draining standing water) and by using mosquito nets and insect repellent to avoid bites.

How this fits together

These are the diseases pathogens cause; the body has its own defences against them, which are the subject of the human defence systems guide.